As one light exposure method for photographic light-sensitive materials, an image-forming method using scanner system is known in which an original is scanned and a silver halide photographic light-sensitive material is exposed according to the imaging signal to form a negative or positive image corresponding to the image of the original.
Various recording apparatuses use the scanner system image-forming described above and recording light sources in these scanner system recording apparatuses, include a glow lamp, a xenon lamp, a mercury lamp, a tungsten lamp, a light emitting diode, etc. However, these light sources have the practical disadvantage of weak output and short life. In order to overcome these disadvantages, some scanner systems use coherent laser light sources such as Ne-He lasers, argon lasers, He-Cd lasers, etc. However, although systems using laser light sources give high output, they have the disadvantages that the- scale of the apparatus is larger, its cost is higher, modulators must be used for the light sources, and also safelights for light-sensitive materials are restricted since visible light is used in these systems, reducing the convenience of operation of the system.
On the other hand, in such applications semiconductor lasers have the advantages that the laser device is small in scale and low in cost, modulation can be easily performed, the life of semiconductor laser is longer than that of the other lasers, and also since such a laser emits light in the infrared region, a bright safelight can be used if light-sensitive materials sensitive to infrared region are used, which improves the ease of handling and operating convenience of the system. However, light-sensitive materials having a high sensitivity in the infrared region that are excellent in storage stability have not yet been developed, and hence the advantages of the semiconductor laser having excellent performance as described above have not yet been utilized in this field.
Commercially available photographic films sensitized in the infrared region, include, for example, HTEI 35-20, a trade name, made by Eastman Kodak Company. Such photographic films cannot be allowed to stand at room temperature and must be stored or placed in a refrigerator or a cold place. As will be apparent from the fact, conventional light-sensitive materials sensitized in the infrared region are unstable in sensitivity, and require specific conditions for storage.
For photographic light-sensitive materials, a spectral sensitizing production technique, is known for expanding the light-sensitive wavelength region of a silver halide photographic emulsion to a longer wavelength by adding thereto a certain cyanine dye. Such spectral sensitizing techniques can be applied in not only the visible region but also the infrared region.
For spectral sensitization in the infrared region, sensitizing dyes having an absorption for infrared light are used and examples of these dyes are described, for example, L in Mees, The Theory of the Photographic Process, pages 198-201 (Macmillan Co., 3rd ed., 1966). In this case, it is desired that the spectral sensitivity, i.e., the sensitivity for light in an infrared region be high and that the change of the sensitivity be as small as possible during the storage of the silver halide emulsions. For these purposes, various sensitizing dyes have been developed, including, for example, those disclosed in U.S. Pat. Nos. 2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921, and 3,582,344. However, even when these conventional sensitizing dyes are used, satisfactory sensitivity in infrared regions and storage stability are not obtained.
On the other hand, it is known that the spectral sensitivity of light-sensitive materials is greatly increased by the addition of certain specifically selected organic compounds in combination with these spectral sensitizing dye(s), which provide a super color sensitizing effect. In general, the addition of a second organic compound to a silver halide emulsion does not increase its sensitivity but instead decreases its sensitivity, and hence the super color sensitization is a quite specific phenomenon, requiring careful selection of sensitizing dye(s) and the second organic compound for use in the combination. Accordingly, even a slight difference in chemical structure greatly influences the super color sensitizing action and hence it-is quite difficult to predict a suitable combination for super color sensitization by chemical structures.
Examples of conventional second organic compounds for super color sensitization include triazine derivatives described in U.S. Pat. Nos. 2,875,058 and 3,695,888, mercapto compounds described in U.S. Pat. No. 3,457,078, thiourea compounds described in U.S. Pat. No. 3,458,318, and pyrimidine derivatives described in U.S. Pat. No. 3,615,632. Also, U.S. Pat. No. 4,011,083 discloses an infrared sensitization using a desensitizing amount of infrared sensitizing dye(s) in combination with an azaindene compound.
By the methods described in these patents, the infrared sensitivity of the silver halide emulsions is certainly increased and storage stability may be improved to some extent, but these improvements remain insufficient, and the development of a super color sensitizer providing a greater increase in infrared sensitivity and improvement of storage stability is desired.
In addition, a silver halide emulsion in a liquid state before coating is subject to fogging and sensitivity changes and, in particular, to such changes caused by the desorption and decomposition of sensitizing dyes. Such deterioration of photographic characteristics in a silver halide emulsion in a liquid state before coating is a large problem in the production of photographic light-sensitive materials. Conventional stabilizers, such as 1-phenyl-5-mercaptotetrazole, etc., are ineffective to improve silver halide emulsions containing infrared sensitizing dye(s), which are in a sol state. Accordingly, a technique for strikingly improving the stability of a silver halide emulsion containing infrared sensitizing dye(s), which is in a liquid state before coating, is desired.